This application claims the benefit of Korean Application No.99-39831, filed Sep. 16, 1999, Korean Application No. 99-45850, filed Oct. 21, 1999 and Korean Application No. 00-12051, filed Mar. 10, 2000, the disclosures of which are herein incorporated herein by reference.
1. Field of the Invention
The present invention relates to an error signal detection apparatus for an optical recording/reproducing system, which is capable of detecting a tilting error signal and/or a tracking error signal, based on the phase characteristics of light reflected and diffracted from a recording medium, with improved accuracy and precision, and a reproduction signal detection apparatus for an optical recording/reproducing system and method therefor.
2. Description of the Related Art
Optical pickups record an information signal on or reproduce an information signal from a recording medium, such as an optical disk seated on a turntable and rotating, while scanning the recording medium in the radial direction. However, if the rotating optical disk is tilted with respect to the optical axis, due to bending of the optical disk itself or error in loading the disk, degradation of a recording/reproduction signal can be caused.
When an optical pickup adopts a light source which emits a shorter wavelength of light, and an objective lens having a high numerical aperture (NA), for the purpose of increasing recording density, comma aberration caused by tilting of the optical disk increases, thereby further degrading the recording/reproduction signal. This is because optical aberration is proportional to xcex/(NA)3.
In an optical recording/reproducing system required for high-density recording and reproduction with a medium, such as a next generation digital versatile disk (DVD), so-called high-definition (HD)-DVD, which has been focused on as a future generation high-density recording medium, there is a need for a tilt error signal detection apparatus capable of preventing degradation of the recording/reproduction signal by detecting the degree of tilting of the disk and correcting for the tilting of the disk based on the result of the detection.
As a conventional tilt error signal detection apparatus, the tilt error signal detection apparatus shown in FIG. 2, which detects tilting of a disk 10 with respect to an objective lens 7, using a signal detected by a photodetector 9 of a general optical pickup as shown in FIG. 1, has been suggested.
FIG. 1 illustrates an example of the optical structure of a general optical pickup. Referring to FIG. 1, a laser beam emitted from a light source 1 for recording and reproducing an information signal is incident on an objective lens 7 through a beam splitter 5. The objective lens 7 focuses incident light from the light source 1 to form a light spot on the recording surface of the disk 10. Light reflected from the recording surface of the optical disk 10 passes through the objective lens 7, is reflected by the beam splitter 5, and goes toward the photodetector 9. Reference numeral 8 indicates a light sensing lens for condensing light reflected by the beam splitter 5 through the objective lens 7 to allow detection of light by the photodetector 9.
The photodetector 9 includes four divided plates A, B, C and D, as shown in FIGS. 2 and 3, for receiving light and performing photoelectric conversion, separately, on incident light. The photodetector 9 sums and/or subtracts the signals detected by the four divided plates A, B, C and D, to detect an information signal and an error signal.
As shown in FIG. 2, the conventional tilt error signal detection apparatus includes a photodetector 9 for use in recording and reproducing an information signal, which consists of four divided plates A, B, C and D arranged in a 2xc3x972 matrix, for receiving light reflected by a disk (not shown) and separately performing photoelectric convention on incident light, first and second adders 11 and 13 for summing the signals generated by the divided plates A and D, and the signals generated by the divided plates B and C, respectively, and a differential unit 15 for subtracting the signals from the first and second adders 11 and 13, and outputting a radial push-pull signal.
The radial push-pull signal output from the differential unit 15 corresponds to a tilt error signal. This radial push-pull signal can be used as a tracking error signal.
The tilt error signal output from the conventional tilt error signal detection apparatus is provided to an apparatus for adjusting relative tilt between the objective lens 7 and the disk 10, and is used in correcting for the tilt error by the apparatus.
The conventional tilt error signal detection apparatus has an advantage of a simple configuration. However, a tilt error signal is detected by subtracting the detection signals of the two groups of the divided plates, which face each other on either side of the central axis aligned in the tangential direction. For this reason, when the objective lens is shifted or when an objective lens-to-disk distance is beyond On-focus positions, the tilt error signal varies with high sensitivity, and thus it is difficult to detect the degree of tilt error with accuracy.
On the other hand, when recording information on or reproducing information from a disk using the optical pickup as shown in FIG. 1, it is required for the optical pickup to accurately trace the tracks of the optical disk. To end this, usually the optical pickup employs a unit for detecting a tracking error signal from the disk by receiving light reflected by the disk after having been emitted from the light source.
As shown in FIG. 3, a conventional differential push-pull detection (DPD) type tracking error signal detection apparatus includes a photodetector 9 for use in detecting an information signal, a matrix circuit 21, two high-pass filters HPF1 and HPF2, two pulse shaping circuits 23 and 25, and a phase comparator 27.
The matrix circuit 21 receives signals a, b, c and d, detected by the four divided plates A, B, C and D, respectively, and sums the detected signals of the diagonally opposite divided plates A and C, and diagonally opposite divided plates B and D, respectively. If a light spot is formed beyond the center of the track, a time delay or a phase difference occurs between the sums (a+c) and (b+d) of the signals. Thus, the amount of tracking error can be identified by detecting the time delay between these signals.
The high-pass filters HPF1 and HPF2 filter off a low-frequency component of the sums (a+c) and (b+d) of the signals output from the matrix circuit 21, and pass only a high-frequency component.
The signals (a+c) and (b+d) passed through the high-pass filters HPF1 and HPF2, respectively, are converted to pulse signals through the pulse shaping circuits 23 and 25. The phase comparator 27 compares the phases of the pulse signals, and outputs a tracking error signal TES"".
The DPD type tracking error signal detection apparatus, which employs the four-section photodetector 9, is adopted to detect the amount of tracking error of the disk in a read only memory (ROM) type disk drive.
Meanwhile, as shown in FIG. 4A, light reflected by the disk for reproduction, after having been focused on the disk, is diffracted into a 0th order diffracted beam and xc2x11st order diffracted beams by pits (P) or marks (not shown) formed on the tracks of the disk 10. Thus, the photodetector 9 receives the 0th order diffracted beam and xc2x11st order diffracted beams, which overlap each other in the radial direction. FIG. 4A illustrates light reflected and diffracted in the radial direction from a high-density disk having narrow tracks. This shows the case where xc2x11st order diffracted beams overlap the 0th order diffracted beam, while separated from each other according to the width of a pit. The signals resulting from the two overlapping portions, i.e., between the 0th order diffracted beam and xc2x11st order diffracted beam, and between the 0th order diffracted beam and xe2x88x921st order diffracted beam, have different phase characteristics from the signal resulting from the 0th order diffracted beam.
If a disk having pits or marks with a relatively large width, three beams, 0th order diffracted beam and xc2x11st order diffracted beams, reflected and diffracted from the disk, may overlap each other in a portion. In this case, the overlapping portion of the three beams, and the overlapping portions between the 0th order diffracted beam and xc2x11st order diffracted beam, and between the 0th order diffracted beam and xe2x88x921st order diffracted beam, show different phase characteristics.
In the case where the disk 10 having narrow tracks for high-density recording, as shown in FIG. 4A, is adopted, along with the reduction of the track pitch, for example, the minimum length of the pit (P) and the minimum interval between the pits (Ps) become short, compared to a general normal density disk (not shown).
As the disk 10 rotates, light is continuously radiated over the pit (P), and the base surface 10a, which is between the pits 10. At the time when the light spot tracing tracks of the disk 10 lands on both a pit (P) and the base surface 10a, interference and diffraction occur between light reflected by the pit (P) and light reflected by the base surface 10a due to the difference in optical paths. As a result, as shown in FIG. 4B, 0th order diffracted beam and xc2x11st order diffracted beams are generated such that they overlap.
Thus, light received by the photodetector 9 includes light from a 0th order diffracted beam and xc2x11st order diffracted beams, which overlap in the track direction, i.e., in the tangential direction. The phase signals in the overlapping portions, i.e., between 0th order diffracted beam and xc2x11st order diffracted beam, and between 0th order diffracted beam and xe2x88x921st order diffracted beam, show different characteristics from the phase signal of the pure 0th order diffracted beam. As shown in FIGS. 4A and 4B, the diffracted beams are complexly overlapping each other and the photodetector 9 receives such complexly overlapping diffracted beams.
As for the conventional tilt error signal detection apparatus shown in FIG. 2, incident light is received by the four divided plates A, B, C and D, and a tilt error signal, i.e., a radial push-pull signal, can be detected from the detected signals. However, the phase characteristics of the detected signals are obscured, and thus the degree of accuracy in detecting the tilt error signals is low.
As for the conventional tracking error signal detection apparatus shown in FIG. 3, the detection signals of the two divided plates A and C, and B and D in the diagonal direction are summed, so that the phase characteristics between the detection signals in the tangential direction are obscured. Thus, in the case where a tracking error signal is detected with the conventional tracking error signal detection apparatus shown in FIG. 3 for high-density recording and reproduction, the phase signals in the overlapped portions can act as noise.
Furthermore, because a high-density optical disk has a narrow minimum pit or mark interval, if interference due to neighboring pits or marks occurs, the level of noise in the tracking error signal can further increase.
Thus, when the conventional tracking error signal detection apparatus of FIG. 3 is employed in detecting a tracking error signal from a high-density disk having narrow tracks for recording and reproducing operations, it is difficult to accurately detect the tracking error signal due to decreased gain and increased noise.
To solve the above problems, it is an object of the present invention to provide an error signal detection apparatus for an optical recording/reproducing system, in which a tilt error signal and/or a tracking error signal can be detected, from a high-density disk having narrow tracks, with high accuracy and precision, in consideration of the phase characteristics of light reflected and diffracted from a recording medium, and a reproduction signal detection apparatus.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the object of the present invention, there is provided an error signal detection apparatus for an optical recording/reproducing system, comprising; a photodetector for detecting an information signal by receiving light reflected and diffracted from a recording medium; and a circuit unit for detecting an error signal by processing detection signals generated by the photodetector, wherein, when the direction of information stream recorded on the recording medium is defined as a tangential direction, and the direction perpendicular to the information stream is defined as a radial direction, the photodetector comprises eight light receiving portions arranged in a 2xc3x974 matrix (2 rowsxc3x974 columns), to separately perform photoelectric conversion on light reflected and diffracted from the recording medium, wherein the rows of the matrix are parallel to a direction corresponding to the radial direction of the recording medium, and the columns of the matrix are parallel to a direction corresponding to the tangential direction, and the eight light receiving portions include four inner light receiving portions arranged at the center region of the photodetector, and four outer light receiving portions arranged around the corresponding inner light receiving portions, and the circuit unit compares the phases of the detection signals of the inner and/or outer light receiving portions arranged in the same row, and outputs a tilt error signal and/or tracking error signal from phase comparison signals.
In another embodiment, the circuit unit amplifies the detection signals generated by the inner and/or outer light receiving portions arranged in a first diagonal direction by a predetermined gain factor, compares the phase of the amplified signal with the phase of the detection signals generated by the inner and/or outer light receiving portions arranged in a second diagonal direction, and outputs a tilt error signal and/or tracking error signal from phase comparison signals.
The present invention provides an error signal detection apparatus for an optical recording/reproducing system, comprising: a photodetector for receiving light reflected and diffracted from a recording medium; and a circuit unit for detecting an error signal by processing detection signals generated by the photodetector, wherein, when the direction of information stream recorded in the recording medium is defined as a tangential direction, and the direction perpendicular to the information stream is defined as a radial direction, the photodetector comprises first through fourth light receiving portions arranged counterclockwise in order in a 2xc3x972 matrix, to separately perform photoelectric conversion on light reflected and diffracted from the recording medium, the first through fourth light receiving portions, wherein the rows of the matrix are parallel to a direction corresponding to the radial direction of the recording medium, and the columns of the matrix are parallel to a direction corresponding to the tangential direction, and the circuit unit compares the phases of the detection signals generated by the light receiving portions arranged in the same row or column, and detects a tilt error signal and/or tracking error signal from phase detection signals.
In another embodiment, the circuit units comprises: first and second delays for delaying the phases of the detection signals generated by the first and second light receiving portions arranged in one row of the matrix, respectively; and a phase comparator for comparing the phase of the sum of the delayed detection signal of the first light receiving portion and the detection signal generated by the diagonally opposite third light receiving portion, and the phase of the sum of the delayed detection signal of the second light receiving portion and the detection signal generated by the diagonally opposite fourth light receiving portion.
The present invention provides an error signal detection apparatus for an optical recording/reproducing system comprising: a photodetector for receiving light reflected and diffracted from a recording medium; and a circuit unit for detecting an error signal by processing detection signals generated by the photodetector, wherein, when the direction of an information stream recorded in the recording medium is defined as a tangential direction, and the direction perpendicular to the information stream is defined as a radial direction, the photodetector comprises eight light receiving portions in a 4xc3x972 matrix (4 rowsxc3x972 columns), to separately perform photoelectric conversion on light reflected and diffracted from the recording medium, wherein the rows of the matrix are parallel to a direction corresponding to the radial direction, and the columns of the matrix are parallel to a direction corresponding to the tangential direction, and the eight light receiving portions include four inner light receiving portions arranged at the center region of the photodetector, and four outer light receiving portions arranged around the corresponding inner light receiving portions, and the circuit unit compares the phases of the detection signals of the inner and/or outer light receiving portions arranged in the same row, and outputs a tilt and/or tracking error signal from phase comparison signals.
Another error signal detection apparatus for an optical recording/reproducing system, comprises: a photodetector for receiving light reflected and diffracted from a recording medium; and a circuit unit for detecting an error signal by processing detection signals generated by the photodetector, wherein, when the direction of an information stream recorded on the recording medium is defined as a tangential direction, and the direction perpendicular to the information stream is defined as a radial direction, the photodetector comprises eight light receiving portions in a 4xc3x972 matrix (4 rowsxc3x972 columns), to separately perform photoelectric conversion on light reflected and diffracted from the recording medium, wherein the rows of the matrix are parallel to a direction corresponding to the radial direction of the recording medium, and the columns of the matrix are parallel to a direction corresponding to the tangential direction, and the eight light receiving portions include four inner light receiving portions arranged at the center region of the photodetector, and four outer light receiving portions arranged around the corresponding inner light receiving portions, and the circuit unit amplifies the sum of the detection signals generated by the inner and/or outer light receiving portions arranged in a first diagonal direction by a predetermined gain factor, compares the phase of the amplified signal with the phase of the sum of the detection signals generated by the inner and/or outer light receiving portions arranged in a second diagonal direction, to detect a tilt and/or tracking error signal.
Another error signal detection apparatus for an optical recording/reproducing system, comprises: a photodetector for receiving light reflected and diffracted from a recording medium; and a circuit unit for detecting an error signal by processing detection signals generated by the photodetector, wherein, when the direction of information stream recorded on the recording medium is defined as a tangential direction, and the direction perpendicular to the information stream is defined as a radial direction, the photodetector comprises first through fourth light receiving portions arranged counterclockwise in order in a 2xc3x972 matrix, and separated in the radial and/or tangential direction, to separately perform photoelectric conversion on light reflected and diffracted from the recording medium, the first through fourth light receiving portions, wherein the rows of the matrix are parallel to a direction corresponding to the radial direction of the recording medium, and the columns of the matrix are parallel to a direction corresponding to the tangential direction, and the circuit unit comprises: an amplifier for amplifying the sum of the detection signals generated by the first and third light receiving portions arranged in a first diagonal direction by a predetermined gain factor; and a phase comparator for comparing the phase of the output signal of the amplifier and the phase of the sum of the detection signals generated by the second and fourth light receiving portions arranged in a second diagonal direction, to detect a tilt and/or tracking error signal.
According to another aspect of the present invention, there is provided an apparatus for detecting a reproduction signal with a photodetector having eight light receiving portions in a 2xc3x974 matrix, four inner light receiving portions arranged at the center region of the photodetector, and four outer light receiving portions arranged around the corresponding inner light receiving portions, wherein, when the direction of information stream recorded on the recording medium is defined as a tangential direction, and the direction perpendicular to the information stream is defined as a radial direction, the rows of the matrix are parallel to a direction corresponding to the radial direction of the recording medium, and the columns of the matrix are parallel to a direction corresponding to the tangential direction, the apparatus comprising: first through fourth delays for delaying a predetermined period of time the detection signals generated by the inner and outer light receiving portions, respectively, arranged in one row; a first adder for summing a delayed detection signal for one of the inner light receiving portions arranged in a first diagonal direction and the detection signal generated by the other inner light receiving portion arranged in the first diagonal direction, and outputting a first sum signal; a second adder for summing a delayed detection signal for one of the outer light receiving portions arranged in the first diagonal direction and the detection signal generated by the other outer light receiving portion arranged in the first diagonal direction, and outputting a second sum signal; a third adder for summing a delayed detection signal for one of the inner light receiving portions arranged in a second diagonal direction and the detection signal generated by the other inner light receiving portion arranged in the second diagonal direction, and outputting a third sum signal; a fourth adder for summing a delayed detection signal for one of the outer light receiving portions arranged in the second diagonal direction and the detection signal generated by the other outer light receiving portion arranged in the second diagonal direction, and outputting a fourth sum signal; and a fifth adder for summing the first through fourth sum signals and outputting the reproduction signal.